Extractability of astaxanthin in a mixed culture of a carotenoid over-producing mutant of Xanthophyllomyces dendrorhous and Bacillus circulans in two-stage batch fermentation

The productivity and extractability of astaxanthin in a mixed culture of Xanthophyllomyces dendrorhous (formerly Phaffia rhodozyma) NCHU-FS501, an astaxanthin over-producing mutant, and Bacillus circulans CCRC 11590 was evaluated in a 1.5 1 fermentor using a two-stage batch fermentation technique. The first stage was for X. dendrorhous cultivation, The second stage was the mixed fermentation of the red yeast and B. circulans. The highest lytic enzyme activity of B. circulans was found at 24 h with yeast nitrogen base (YNB) as the nitrogen source and incubation at 30 degreesC in a pure culture, The induction of B. circulans lytic enzyme activity was influenced by the cell wall concentration of A. dendrorhous. The fastest induction was observed with addition of 2.5 g/l cell wall, The cultivation time in the first stage of fermentation significantly affected the extractability of carotenoid in the second stage of fermentation. Minimum extractability was found when X. dendrorhous was cultivated for 96 h in the first stage. Glucose concentration of 45 g/l in YNB supported high X. dendrorhous growth and astaxanthin production, with astaxanthin production of 9010 mug/l was observed during the first stage, Although the red yeast produced more astaxanthin with peptone as nitrogen source during the first stage, YNB supported the highest extractability of carotenoid and lytic activity of B. circulans in the second stage of fermentation. The optimal pH and temperature for pigment extraction in the mixed culture were pH 6.5 and 30-34 degreesC respectively. Under these conditions, about 97% of the total pigment could be extracted after a 48 h incubation time. When the crude enzyme was recycled in the mixed culture, lytic enzyme activity of 20 units/ml was obtained after one incubation cycle (48 h), with 69%, of total carotenoids extracted. (C) 2002 Elsevier Science Ltd, All rights reserved.